There were reportedly many Afghan National Army soldiers inside the bank at the time of the explosion.

Emergency workers and passersby tried to help the injured, who were strewn among the dead. Ambulances and private cars ferried the victims to hospitals.

"Civilians and military are among the wounded," Zwak said.

There was no immediate claim of responsibility for the attack.

Al Jazeera's Rob McBride, reporting from Kabul, said the New Kabul Bank had been targeted before,

"It handles salary payments for security forces," he said.

"Because it has been targeted before, it does have very tight security. But there's only so much you can do with a car bomb outside."

Afghanistan: Bullets And Burqas

Last month, at least three people were killed and many wounded in an attack on a bank in the eastern city of Gardez.

In a similar attack in February, at least six people were killed when a Taliban bomber rammed an explosives-laden car into Afghan soldiers who had queued outside a bank in Lashkar Gah to collect their salaries.

The Taliban effectively control or contest 10 of the 14 districts in Helmand.

Intensified fighting last year forced thousands of people to flee to Lashkar Gah from neighbouring districts.

Since they launched their spring offensive in late April, the Taliban have been mounting lethal assaults on the Afghan army and police outposts in Helmand.

Washington is expected to announce an increase in the US military deployment to bolster Afghan forces.

US troops in Afghanistan now number about 8,400, and there are another 5,000 from NATO allies, a far cry from the US presence of more than 100,000 six years ago. They mainly serve as trainers and advisers.

Pentagon chief Jim Mattis this month acknowledged that America still is "not winning" in Afghanistan nearly 16 years after the US-led invasion toppled the Taliban regime.